Gold and silver can be recovered from an ore containing same by comminuting the ore and treating the subdivided product with a lixiviant in the form of an alkaline cyanide solution in tanks to which air is supplied to raise the oxygen content of the leaching solution. Such systems are described by Victor Tafel, Lehrbuch der Metallhuenkunde, 1951, volume 1, pages 31 to 34.
The residence times in the tank for the solids are extremely long, e.g. 20 to 40 hours, for high yields or recoveries.
It is also known that the solubility of gold increases with increasing partial pressure of oxygen in the leaching solution and falls after having reached a maximum (see page 17 of the Tafel publication mentioned previously). In Engineering and Mining Journal, volume 140, No. 1, 1939, pages 44 through 46, investigations with an oxygen partial pressure of 0.21 to 8.3 bar have been described and it is here pointed out that under these conditions maximum solubility is exceeded.
Apparently this teaching or knowledge of this fact has limited attempts to utilize superatmospheric pressure in leaching systems for the purposes described inasmuch as one could not expect, based upon these teachings, any increase in the gold or silver solubility and indeed from the earlier knowledge with respect to peaking of the solubility, one would expect a decrease in solubility to follow the maximum described by Tafel.